Optics: measuring and testing – Range or remote distance finding – With photodetection
Reexamination Certificate
2002-11-14
2003-12-16
Tarcza, Thomas H. (Department: 3662)
Optics: measuring and testing
Range or remote distance finding
With photodetection
C356S005010, C342S070000, C342S092000, C342S091000
Reexamination Certificate
active
06665056
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a radar apparatus for measuring a distance to a detection object by using the well-known sensitivity time control (STC) technique, and more particularly to a technique of correcting, with raised accuracy, errors caused by the STC and dependent on the intensity of reflected waves.
2. Description of the Prior Art
FIG. 1
is a diagram showing how the received reflection signals are STC amplified in an STC-based radar system for determining the distance or range from the radar system to a target object. In such a system, the amplification factor (A.F.) of an STC amplifier is varied with the period of time from the emission of a transmission signal to the reception of the reflected transmission signal as shown in FIG.
1
.
FIG. 1
also shows pulse waveforms of received reflection signals Vi
1
and Vi
2
received at times t
1
and t
2
measured from the emission of respective transmission signals and STC-amplified versions Vo
1
and Vo
2
of the received reflection signals Vi
1
and Vi
2
, respectively. In this case, as is well known in the art, the STC-amplified reflection signals Vo
1
and Vo
2
are distorted in the STC process. The distortion causes an error (denoted by “&bgr;”) between the peak position Tip of a pre-STC-amplification received reflection signal Vi and the peak position Top of the STC-amplified received reflection signal Vo. This error &bgr; (=Vop−Vip) is hereinafter referred to as “STC-distortion error”. The shorter the distance or the signal transit time between the radar system and the target object is, the larger the STC-distortion error is as shown in FIG.
1
. Thus, the STC-distortion error &bgr; depends on the signal transit time.
However, even if the distances to reflection objects are identical to each other, the intensities of refection signals from the reflection objects in a same range may vary depending on the reflectance of the reflection objects.
FIG. 2
shows how the STC distortion of STC-amplified reflection signal is affected by the intensity of the received reflection signal. In
FIG. 2
, waveforms labeled “L” are for reference reflection signals of a predetermined level.
FIG. 2A
shows, for a smaller reflection signal, a pre-STC-amplification reflection signal Vsi and the STC-amplified version Vso of the signal Vsi.
FIG. 2B
shows, for a larger reflection signal, a pre-STC-amplification reflection signal V
L
i and the STC-amplified version V
L
o of the signal V
L
i. In
FIG. 2
, Vr is a reference voltage for determining the start timing and the end timing of each reflection signal. The error in the rising edges of the reference reflection signal L and each of the STC-amplified reflection signals Vso and V
L
o consists of a first error component D
1
due to the intensity of the reflection signal and a second error component D
2
due to the STC distortion. If the middle point Tc of the pulse width at the reference voltage Vr is calculated as the peak position Top of each STC-amplified reflection signal Vo, the peak position Top of each STC-amplified reflection signal Vo depends on the STC distortion and the intensity of the reflection signal. (The intensity of a reflection signal can be estimated by the pulse width measured by using the reference voltage Vr.) In other words, even if reflection objects are in an identical range, the peak positions of STC-amplified reflection signals from the reflection objects vary in response to the intensity of the STC-amplified reflection signals. Hereinafter, the error between the peak position of an STC-amplified reflection signal and the correct peak position (i.e., the time interval from which the true distance is calculated) is referred to as an “error due to received signal intensity” or “&agr; error”. Since the STC distortion error component D
2
is an error in the rising edge, the error of the middle time Tc is equivalent to the arithmetic average of STC distortion error components in the rising edge and the falling edge.
From the foregoing description, it is seen that the above-mentioned STC-distortion error &bgr; depends on not only the signal transit time but also the intensity (or the measured pulse width) of a reflection signal.
Therefore, what is needed is a method and a system for correcting an error due to waveform distortion caused by an STC process in distance measurement by using a correction value determined not only by the signal transit time but also by the intensity (or the measured pulse width) of a reflection signal.
Also, what is needed is an STC-based radar apparatus that corrects an error due to waveform distortion caused by an STC process in distance measurement by using a correction value determined not only by the signal transit time but also by the intensity (or the measured pulse width) of a reflection signal.
There have been proposed various error correction techniques for distance measuring systems.
For example, U.S. Pat. No. 5,805,527, which is a counterpart of Japanese Patent Application Publication No. 9-236661 (1997), discloses “Method and apparatus for measuring distance”. Though the patent deals with an error caused by variation in the intensity of the reception signal, it does not mention the above-described STC-distortion error.
Japanese Patent Application Publication No. 7-71957 (1995) discloses a distance measuring apparatus. The distance measuring apparatus corrects an error due to the STC distortion. However, the error correction is done with a correction value determined only by the signal transit time or the distance between the apparatus and the reflection object.
Thus, the prior art has failed to meet the above-mention needs.
SUMMARY OF THE INVENTION
According to an aspect of the invention, the above-mentioned problems are solved by a method of measuring a distance to a reflection object in a radar apparatus that transmits a transmission signal and applies a sensitivity time control (referred to as “STC”) process to a reflection signal from said reflection object to yield an STC-processed reflection signal. In the method, a quantity corresponding to the distance is obtained from a transmission time of the transmission signal and a detection time of the STC-processed reflection signal. The quantity is corrected considering an error which is caused by an STC distortion and depends on the intensity of the STC-processed reflection signal.
The correction of the quantity is achieved by correcting the quantity by using a first correction value associated with the intensity of the STC-processed reflection signal to provide a corrected quantity; and correcting the corrected quantity by using a second correction value associated with the corrected quantity and the intensity of the STC-processed reflection signal to correct the error regardless of the intensity of the STC-processed reflection signal.
The above-described method is preferably realized by a computer program. The computer program may be stored in a computer-readable storage media such as a flexible disc, a hard disc, a magneto-optical disc, CD-ROM, ROM, etc. and is loaded into a system RAM for execution if necessary. Alternatively, the computer program may be loaded into a system RAM via any network.
According to another aspect of the invention, there is provided a radar apparatus for measuring a distance to a reflection object. The apparatus transmits a transmission signal by using a laser diode for example and applies a sensitivity time control process to a received signal from the reflection object by using, for example an STC amplifier to provide an STC-processed signal. The radar apparatus includes a controller. The controller obtains a quantity corresponding to the distance from a transmission time of the transmission signal and a detection time of the STC-processed signal; and corrects the quantity considering an error which is caused by an STC distortion and depends on the intensity of the STC-processed reflection signal. The controller corrects the quantity in the above-described manner.
The radar apparat
Matsuoka Keiji
Morikawa Katsuhiro
Nozawa Toyohito
Samukawa Yoshie
Shirai Noriaki
Andrea Brian
Denso Corporation
Posz & Bethards, PLC
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